The ice cap has a diameter of about 1000 km and consists of many thin layers of ice mixed with dust that extend to a depth of around 2 km below the cap. The prominent gap in the ice cap is a 318 km-long, 2 km-deep chasm called Chasma Boreale.

The layers result from variations in the orbit and rotation of Mars that affect the amount of sunlight received at the poles, and thus the amount of melting and deposition of materials over time. Meanwhile, strong prevailing winds are thought to be responsible for shaping the spiral troughs.

The polar ice cap visualized in this video was created using data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument—MARSIS to its friends—which uses low-frequency radio waves to visualize interfaces between layers of different materials underground. Clearly it works pretty well, because the results are beautiful. [ESA]